Gaseous discharge device



June 16, 1931. RUBEN GASEOUS DISCHARGE DEVICE Filed July 2, 1927 Mgall/11 v v I awvewiioi Patented June 16, 1931 UNITED STATES SAMUELRUBEN, OF NEW YORK, N. Y., ASSIGNOR TO RUBEN PATENTS COMPANY, OF

PATENT OFFICE NEW YORK, N.,Y., A. CORPORATION OF DELAWARE GASEOUSDISCHARGE DEVICE Application filed July 2, 1927. Serial No. 203,035.

This invention relates to gaseous discharge devices and moreparticularly to the use of such devices in the rectification ofalternating currents.

- efficient current output capacity of an ionic rectifying devicewithout necessitating an increase in size of parts.

Briefly these ob ect-s are accomplished by the provision of a cathode,which comprises substantially a reacting surface composed of highlyelectro-positive and readily volatile metal applied to a base ofmetallic material which will react with compounds of the surface metalto cause their reduction and thus maintain the surface metal in a purestate. With the use of such a cathode, there is produced a device whichpossesses a particularly low operating impedance and high currentcapacity resulting from the concentrated field of metallic vaporsurrounding the electrodes and produced by volatilization of the cathodesurface metal under the influence of the heat generated at theelectrodes and the electrode bombardment by gas particles and also fromthe photo-electric action at the surface metal producing electronemission. Furthermore, such a device also possesses a low ionization ordischarge potential, a low cathode drop of potential, and long liferesulting from the maintenance of greater gas purity and from thereduction of the gas losses such as result from chemical absorption andphysical adsor tion or both.

nother feature is that of supplying the low pressure initiallyconductive gas at a pressure somewhat in excess of that value givingminimum impedance to thereby extend the life of, the device over alonger period, as the reductions in pressure attendant upon operation ofthe device will then lower the pressure to a value approaching that ofminimum impedance and thus actually lower the impedance, in contrast tothe increased impedance which results from the decreased pressure causedby gas loss when the initial pressure value is equal ,to thatcorresponding to min'mum impedance. Since these losses occur principallyearly in the life of the (leviee, the latter will thus possess a minimumoperating impedance during the greater portion of its life.

A further feature of the invention comprises the use of an auxiliary.electronemissive filament in combination with the usual cathode elementand placed transverse to and within the leakage current path between theelectrode pairs of a full-wave rectifier. With such an arrangement theleakage current heats the auxiliary emissive filament, causing it toemit an electron stream tending to cause greater ionization of theconducting gas particles and thereby materially increase the currentoutput or load which the device will carry and appreciably decrease theinternal impedance and dependence of the operating characteristics ofthe device upon the gas pressure.

'To these and other ends, the invention consists in further features allof which will be more fully described and thoroughly understood with theaid of the description to be given in connection with the accompanyingdrawings, the novel features being particu larly set forth in theappended claims.

In the drawings:

Fig. 1 is a vertical sectional view of a full wave rectifying devicecomprising two pairs of electrodes constructed inaccordance with theinvention and shown connected in circuit with a transformer for securingfullwave rectification;

Fig. 2 is a vertical sectional view taken along the line 2" x of Fig. 1;

Fig. 3'is a horizontal sectional view taken along the line 33 of Fig. 1;

Fig. 4 is a perspective view, partly broken away of the preferredelectrode arrangement;

Fig. 5 away, of a modified form of electrode;

Fig. 6 is a vertical sectional view of another alternate form ofelectrode;

Fig. 7 is a horizontal section taken along the line PF-7 of Fig. 6; and

is a perspective view, partly broken wave rectification of "alternatingcurrents.

The particular device illustrated and described hereinafter is'oneshowing the adaptation of the invention to a rectifying deviceespecially suited for use in supplying the necessary rectification inthe filter. circuits in so-called l3 battery eliminators used inconjunction with radio apparatus. Generally, such a device comprises asuitable glass bulb or envelope 10 containing a readily ionizablegaseous atmosphere at low pressure and havingan inner upright glass post11 7 formed integral'thercwith and serving as a support for two. similarsets of'associated anodes 12, 12a and cathodes 13, 13a. The

anodes are provided with separate lead-in wires 14 and 15 while thecathodes are joined internally and provided with a common leadin wire16, all lead-in wires 14, 15 and 16 being sealed in the post 11 andjoined as by spot welding to the ends of their respective electrodes.\Vith this arrangement, complete or full-waverectification is thenobtained by connecting the anode leads 1 1 and 15 to the ends of thesecondary of a suitable transformer 17 whose primary is connected acrossthe incoming alternating current lines 18 and 19, the direct currentbeing taken oil through leads 20 and 21 connected respectively to thecentral point of the secondary and the cathode lead-in wire 16. Thus,the

cathodes are at all times negative to one of the anodes and positive tothe other, this designation or relation changing'at the end of eachhalf-cycle, so that current flows alternately through each pairof-electrodes producing a continuous uni-directional current in thedirect current leads 20 and 21.

Rectification in this form of device is obtained principally by the useof spaced electrodes of dissimilar surface areas, producing therebyasymmetrically conductive electrode gaps and resulting in a greater flowof positive current from the smaller to the larger surfaced electrodeand the amount of rectification is substantially dependent upon thesputtering at the electrodes and the resultant occlusion of gases.

Electrode combinations of various designs may be employed to provide thedesired surface'area ratio but I have found the use of a short tubularmember having a cylindrical cavity and open at at least one end incombination with a rod positioned in axial alinement therewith with oneend projecting within the open end of the former togive especiallysatisfactory results. With this arrangement asymmetrical conductivity,giving rectification, is produced and is dependent upon the size of theelectrodes or in other words, their diameters, and upon the length ofthe rod electrode protruding within the cylindrical electrode. Since thegreater positive current flows from the smaller to the larger electrode(a larger flow of negatively charged particles taking place in thereverse direction), the cylindrical electrode may be appropriatelytermed the cathode and the smaller or rod electrode the anode, as whenthe polarity relation between the electrodes changes from thisdesignation, there is no appreciable flow of current between them.

In the device illustrated, the rod anodes 12, 12a are suitably secured,as by sealing, with their axes vertical to the glass post 11 and areenclosed within suitable refractory insulating jackets 22, 22a as abaked lava product, so as to leave active only a small portion of theirsurfaces adjacent the cathodes and thereby suppress the ionic dischargefrom the anodes and thus obtain the desired surface area ratio betweenanode and cathode. By forming the refractory jackets 22, 22a with flatupper surfaces and of similar cross-section to that of thetubularcathodes 13, 13a, the latter may be conveniently supported on theformer. In order to restrict the ionic discharge to the desired pathsand reduce leakage, the cathodes are preferably enclosed with suitablemetallic tubes 23, 23a extending beyond the upper ends of the cathodesand these tubes are conveniently supported on external lateral annularshoulders 24 provided on refractory jackets 22, 22 just below theirupper ends. Semi-rectangular braces 25 are welded to the tubes 23, 23ato add stiffness and a further support is provided in the form of avertical metallic rod 26 having its lower end sealed into the glass post11 and its upper end connected as by welding to a cross-piece 27 joiningthe two cathode tubes 23, 23a. By securing the c'athode lead-in wire 16to the end of this support 26, the cathodes are suitably connected in.circuit.

The operating characteristics of an ionic discharge rectifying deviceare substantially dependent upon the discharge potential, or thepotential required to start the discharge when the circuit is closed,and the impedance of the device, the device being constructed anddesigned as to make both these factors a minimum. The initial dischargepotential. is dependent upon the ease with which the conductin operatingimpedance is substantially dependent upon the conductivity of the mediumafter initial ionization. The impedance is also dependent upon thepressure of the aseous conducting medium, the cathode rop of potential(a property of the cathode-surface metal), and the purity of the gas andelectrode surfaces.

Certain of the factors thus noted are not constant but show a tendencyto so change with time as to increase the impedance and the life of thedevice is thus decreased since it is substantially determined by therate of increase of the impedance. The presence of impurities in thetube not only adds to the initial impedance value but also causes anincrease in the same by interacting with other elements to form newcompounds and also with the conducting medium per se to decrease itsconductivity. Sputtering at the electrode surfaces, which occurs whenthe latter become heated under impact of the gas molecules, causesocclusion or absorption of the gaseous medium, results in reduction ofgas pressure with the consequent increase in impedance, and also causesdestruction of the electrodes per se.

In accordance with a feature of my invention, I have overcome the abovenoted difficulties by forming the cathode reacting surface of a readilyvolatile highly electro-positive metal and employing an easily ionizableand preferably inert gas as the conductive gaseous medium. With thiscombination of features the inert gas will serve as the initialconducting medium by means of which the discharge is started, providingthe device .thereby with a low discharge potential, and

under such operation the readily volatile metal is vaporized, forming anatmosphere of especially high conductivity which will serve to carry theload during the balance of the operation, thus materially reducing theimpedance during operation. Furthermore with such a cathode surface ofan electropositive metal the cathode drop of potential is reduced to aminimum and similarly sputtering with absorption of gases and consequentreduction of gas pressure and increase in impedance is also reduced to aminimum. Also by using such an alkali metallic vapor as the loadcarrying conductive medium, the device is less dependent upon thepressure of the inert gas (since the operation is no longer dependentpurely upon the gas ionization under the direct influence of the appliedpotential) and small changes in the gas pressure will consequently notmaterially affect the opearting characteristics and life of the device.I have also found that the use of electro-positive metal surfacedcathodes promedium may be ionized while thecreasing the e which willreact by gas discharge and electrode bombardment thus creating a greaterionization of the gaseous atmos here and consequently inciency andoutput capacity. A cathode surface of highly electro-positive metal maybe supplied in various ways,

but I have found that the usual ditliculties incident to the handlin andworking of such metals (due to their highly active chemical nature) aresatisfactorily overcome by-forming the cathodes 13, 13a of a metallicmaterial readily with compounds of the desired surface metal to causetheir reduction, coating-such a base prior to exhaustion of the devicewith the surface metal in the form of one of its suitable stablecompounds, and heating the coated base after exhaustion and prior tofilling, as inductively, to cause the reduction of the compound, leavingthe base coated with a regular uniform surface of the desired highlyelectropositive metal in the free state. In this man ner, any compoundsof the electro-positive metal formed during operation by its interactionwith impurities are quickly reduced and the surface at all timesmaintained in a pure state. Magnesiumhas been found to be a particularlysatisfactory metal for use as a cathode base, since it possesses a readytendency to cause reduction of other metals and furthermore in theinstant application, it

serves the additional function of serving in place of the usual getterto purify the gaseous atmosphere. The electro-positive metal employed ispreferably that possessin the lowest practicable atomic number an theproperties desired are possessed by the alkali metals of the first groupof the periodic system of elements which include caesium, rubidium,potassium, sodium and lithium, the arrangement being in their order .ofpreference from the operating characteristic viewpoint. When caesium orrubidium is employed, for example, the surface is'suitably obtained bycoatlng a magnesium base 13, 13a with a layer of caesium or rubidiumchloride and heating to reduce the latter and form the pure metal,caesium or rubidium, as the case may be. The amount of caesium orrubidium provided may be varied within wide limits but I have found thata coating or approximately 0.1 mms. depth to give excellent results.

In'ionic discharge devices, the impedance is directly dependent upon thegas pressure and even small variations in either direction from acertain definite pressure corresponding to minimum impedance producecomparatively large increases in the impedance and discharge orionization potential characteristics. It is customary therefore, toaccurately control the pressure within the tube so as to obtainapressure giving minimum On the other hand, however, I

that reductions in the gas conimpedance. have found tent, accompanied bycorresponding 1ncrcases in impedance, occur during the operation of thedevice, such losses being caused principally by sputtering at theelectrode surfaces, causing occlusion of the gases.

In order to counter-balance these undesirable characteristics andthereby extend the life of the device, I supply the inert gas at apressure somewhat in excess of that correspondin to minimum impedance,so that should rediiction of the active gas content oeeur (as byocclusion or absorption due to sputtering at the electrodes) thepressure will be lowered to the desired minimum impedance value. Thelife of the device is thereby materially extended, since a greaterdecrease in pressure due to this occulsion occurs during the earlystages of the operation, the rate of loss being smaller thereafter, andby employin an initial pressure above the desired minimum impedancevalue this initial drop will cause a decrease in pressure to a valueapproximating the minimum impedance value instead of a decrease to avalue below the minimum impedance value. Consequently the device willpossess during the greater portion of its life an impedance value morenearly approximating that of the desired minimum impedance value and asa result thereof, the life will be appreciably extended.

The particular value of gas pressure employed will depend upon theallowable leakage current which may exist, since the use of a higherpressure results in increased leakage. As a general rule, however, Ihave found that the leakage current will be maintained within suitablelimits, if the gas pressure employed is not greater than ten per centabove the minimum impedance value.

The choice of gas to be employed as the initial conducting medium willbe determined by a consideration of the operating characteristics of agiven gas together with the commercial and economic feasibility of itsuse. The various characteristics which such a gas should preferablypossess comprise:

1. Stability under the operating conditions of the device.

2. A substantially inert or non-reactive character relative to the otherelements present in the device.

3. Low ionization potential, or in other words high electricalconductivity, to pro vide the device with a low discharge potential andlow impedance.

4. Low atonic weight to decrease the bombardment efiects on theelectrode.

Those gases which I have found to be best suited for general use inionic discharge devices are the monatomic gases, neon, helium, argon,all of which are stable and substantially chemically inert, and of theseneon and helium are the more preferable for use in such circuits as Bbattery eliminator circuits for radio installations, the choice betweenthese latter being obtained by a study of comparative operating datatogether with costs of materials. Helium, for example, is the lightergas and will therefore result in a smaller bombardment effect on theelectrodes, thus diminishing sputtering and gas absorption at theelectrode surfaces. Noon, on the other hand, is appreciably moreconductive than helium and is less critical with respect to the relationbetween the gas pressure and impedance of the device, thus makingpossible the use of a greater excess of gas, to offset sputtering andocclusion losses, without appreciably afl'ecting the impedance.

In Fig. 5, I have shown a modified arrangement of the electrodes inaccordance with my invention and in which the cathodes comprise flatplate electrodes 28 of a metal having a low cathode drop of potential,as nickel or aluminum, supported on the shields 29 perpendicular to theaxis of the rod anodes 30 and provided with a small central opening 31disposed in axial alinement with the anode and serving to equalize orbalance the discharge between the electrodes. The alkali vaporconducting medium is provided in this form of the invention bydepositing the metal upon the interior parts of the device in such amanner that it will be vaporized under the influence of the heatconveyed to it by radiation and convection from the electrodes. As inthe case of the vapor produced from the coated cathode, the metallicvapor here produced will serve to carry the load during operation, thusproviding the device with a low operating impedance. vapor constituentis preferably deposited within the device as the last step in itsproduction so that loss of the vapor during the earlier steps of bakingand evacuation is obviated. I accomplish this end by using the metal inthe form of a compound mixed with a reducing agent which will liberatethe metal upon the application of heat and placing such a mixture in asuitable container, as a metallic capsule 32 carried on suitable wiresupports 33 above the electrodes. With this construction the other stepsin the production of the device may be carried out without volatilizingthe metal and then the metal de-. posited, as the final step, on theinterior parts of the device by heating the capsule, as inductively, toa temperature sufliciently high to cause reduction of the desired metalcontaining compound and volatilization of the reduced metal. WVhencaesium is employed as the conductive vapor, for example, I employ apowdered mixture of caesium chloride and metallic magnesium in thecapsule 32, and upon heating such a mixture, the interaction of thesematerials produces magnesium chloride and caesium which latter thenvola- The metallic tilizes and upon coolin condensers upon the solidportions of the tu e and particularly in the field of discharge of thedevice such as on the walls of the cathode and the cathode shield. Inthis way a concentrated field of the vapor is obtained in the immediateareas of the electrodes.

To increase the output of an ionic discharge device has been the objectof a further feature of the invention and in accordance with thisfeature, I have found that the current capacity may be greatly increasedand at the same time the over-all efliciency, even at low currentvalues, greatly increased by employing a thermionically active elementor filament 34 (Fig. 5) in circuit with the cathode and positionedtransverse to and within the leakage current path which normally existsbetween the electrodes of a full-wave rectifying device employing twopairs of electrodes for rectification of both sides of each wave. I havefound that this leakage current is of such intensity that articlesplaced transverse to and within its path become readily and quicklyheated to a temperature which decreases with the distance away from theelectrode, and is sufficient to create a bright red heat in closeproximity to the electrode. With such a thermionic element as anauxiliary cathode, the leakage current thus causes it to become heated,resulting in an emission of electrons which are attracted along to theanode and cause ionization of the. gaseous molecules, therebyappreciably increasing the current carrying capacity of the device.Furthermore since there is thus supplied an auxiliary source ofelectrons for gas ionization, the device is considerably less dependentupon the inert gas pressure. When the current reverses during the otherhalf of each cycle the filament becomes positive with respect to the rodanode and no current flows as the emitted electrons, being negativelycharged, will be repelled by the negatively charged anode. Furthermore,by changing the position of the auxiliary thermionic cathode 34 in theleakage path so as to vary its distance from the anode, the amount ofemission may be readily controlled since the emission is dependent uponthe temperature of the filament which in turn varies with its distancefrom the anode. When such an auxiliary cathode is included, the leakagecurrent set up will quickly heat the filament 34, causing emissiontherefrom and emitted electrons will in turn cause an increasedionization of the gas particles.

In addition the cathode and anode drops of potential are also materiallyreduced and particularly as a result of these effects the impedance isgreatly lowered. Thus the use of a thermionically active filamentarycathode in an ionic discharge device increases the current carryingcapacity of the device and with lower capacities materially increasesthe eficiency. In addition, the life of the device'is materiallyincreased.

In the electrode arrangement illustrated, I have shown the thermionicauxiliary cathodes as short coiled thermionically active wires 34,supported as by spot welding on the upper surfaces of theplate cathodes28, over the openings 31 therein/ These openings 31 in this formof'elefirode in whichan auxiliary thermionic element is employed affordconvenient and direct passages for the emitted electrons to the anode.Various materials may be employed to provide the thermionically activeelement, but I have found that the use of conductive cores coated withthermionically active materials such as the oxides of the alkali earths(barium, calcium and strontium,) or mixtures of them with each other orwith other materials to be especially satisfactory.

In Fig. 8, I have shown the adaptation of the arrangement of Figs. 1, 2,3 and 4 to a one way rectifying device, containing but one electrodepair, together with suitable circuit connections for its use.

A modification of the preferred electrode structure is shown in Figs. 6and 7, the oathode being shown as a plate 37 provided on one edge with alateral flange by means of which it is secured to and supported withinthe shield 38 in spaced relation to the rod anode 39.

In assembling the various elements in the production of the device, careshould be taken to insure purity and cleanliness of all parts andelements since the ionization potential and impedance are increased bythe presence of impurities whose action might be either to raise theionization or break down potential, to increase the anode and cathodedrops of potential and therefore the impedance, due to chemical reactionat the surfaces of the electrodes, or it might be acombination of boththese effects. The gas purity may be readily controlled either prior tothe filling of the tube by the insertion of a hot magnesium electrode orgetter in the path of the inflowing gas or after filling by includingsuch a getter in the arrangement of the device. When the alkali vaporconduction feature, however, is employed, the alkali metal will, insputtering and during volatilization, tend to purify the gas, obviatinthe necessity of employing a getter.

ince the discharges take place uponthe surfaces of the electrodes andvolatilization of the alkali metal is eifected from all parts orsurfaces within the device, these parts should be thoroughly cleanedbefore use.

What I claim is v 1. An ionic discharge rectifying device comprising twopairs of spaced asymmetrically conducting electrodes of oppositepolarity, and an electron emissive filament in direct electrical con c wth a catho e e1ectrode and positioned in the leakage path of the deviceto be heated by the leakage current.

2. An ionic discharge rectifying device comprising two pairs of spacedconducting electrodes of opposite polarity, and an electron emissivefilan'lent in direct electrical contact with a cathode electrode andpositioned in the leakage path of the device at predetermined distancefrom the anode e; trode, said filament to be heated by the leakagecurrent.

3. An ionic discharge rectifying device comprising an enclosingenvelope, two pairs of opposed electrodes to provide full-waverectification, the members of each pair being spaced apart relative toeach other, leads for the electrodes, and an electron-emissive electrodein direct electrical contact with a cathode member and disposed in theleakage path between the electrode pairs to be heated by the leakagecurrent.

This specification signed and witnessed this 28th day of June 1927.

sAMUEL RUBEN.

